ADF4158 PLL strange moving spurs

Posted on Feb 6, 2014

On the 10 MHz fundamental I only measure the HP8562E PN flloor meaning that the TCXO phase noise is better than the spectrum analyzer noise floor. I`ve measured some harmonics from 20 MHz to 1 GHz. There are still measurable harmonics up to 2-3 GHz. 2. TCXO Slew rate have been measured at about 2. 5~3ns/V = 400V/us which

ADF4158 PLL strange moving spurs
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is the minimum requirement or slightly lower. I`ve tried different sources without any change in the output phase noise. An improve might be to use an ECL gate for instance between the TCXO and the ADF to drive the REFin, right 4. apprently yes the ref pin on the opamp seems clean. It`s derived from P3VA with a bridge resistor. This is a modification brought on the prototype as the schematic above show a connection to GND. I`m going to add a capacitor on it to improve if needed. 5. Figure below is the PLL chip on top and the OP184 on bottom. tracks are short, grounding made as short as possible. On things which might be improved, the PCB which contains mixed parts has one GND plane only. I`ve tried to ensure that dirty and clean signals do not mix by locating them properly, but this could indeed be not enough. But I do not measure things on P3VA side.

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